I know that recently general aviation planes were allowed to fly into National Airport once more, but even now I'd say there are less than 5 or 10 GA flights per day, whereas before 9/11 there were several hundred. While GA flights will never approach the pre 9/11 level, will they ever get higher than they are now?

DCA currently allows a maximum of 48 GA flights per day. Furthermore, the passenger and crew manifest has to be submitted to and approved by TSA at least 24 hours in advance, and the flight has to originate (or stop off) at one of 12 designated "pre-screening" airports where the aircraft, passengers, and baggage get screened for security as they would for a commercial flight.

So while theoretically DCA could see up to 48 GA arrivals per day, I doubt even that limit will be approached while the current onerous security process is in place. Frankly, I'm surprised that even 5 or 10 operations per day are willing to undergo the process as opposed to simply flying to another airport nearby.

Don't forget about the requirement of having to pick up an air marshall at the gateway airport and then the company operating the aircraft has to reimburse TSA for the cost of the screening and air marshall.